(a) Field of the Invention
A hydraulic raising apparatus with automatic regulated speeds comprises additional hydraulic circuits, check valves and adjustable relief valves arranged between the piston rod side chamber and the rodless side chamber of hydraulic cylinders and pumps. The arrangement enables hydraulic cylinders and pumps to change their role in circuit, depending on loaded conditions, from a piston to a spool and vice versa. Hence the hydraulic apparatus can adjust its raising speeds in agreement with loads. When a load is light the apparatus can quickly carry it to position. On the other hand, when the load is heavy the apparatus will gradually move it with reduced input energy.
(b) Description of the Prior Art
A conventional hydraulic raising apparatus, the so-called jack, primarily comprises a working cylinder, a piston rod, a hydraulic pump, a reservoir, a return valve (or release valve), a safety valve and connection circuits. The piston rod is provided on the outer end with a raising arm. In operation a rocker or handle is usually pulled and pushed to pump hydraulic fluid into the working cylinder and drive the piston rod to raise a load.
In such a conventional structure, it does not have variable speeds for different loading conditions. The same speed occurs either at no load or in a light or a heavy load condition. Consequently users must operate the handle repeatedly to activate the working cylinder until the load is moved by the raising arm to a desired position. The raising speed does not vary in agreement with the apparatus's load condition. It not only wastes time and but also leads to a low working efficiency. Users must spend more energy to operate. Evidently an invariable speed can not satisfy users' need. It is desirable to have improvements made on conventional structures.